Public Comment Number PC-UK0267 ISO/IEC CD2 9899 (SC22N2794) Public Comment =========================================== Date: 1998-09-22 Author: N.M Maclaren Author Affiliation: Self Postal Address: University of Cambridge, Computer Laboratory, New Museums Site, Pembroke Street, Cambridge CB3 3QG, United Kingdom E-mail Address: Telephone Number: +44 1223 334761 Fax Number: +44 1223 334679 Category: Normative change to existing feature retaining the original intent Committee Draft subsection: 6.2.6.2 Title: Problems with multiple zero representations etc. Detailed description: PC-UK0122 and other public comments raised some serious problems with multiple representations of zero, but the FCD has addressed only some of them. The remaining comments in PC-UK0122 have been separated out, and this is one of them. The current wording forbids the all-ones representation in ones' complement and negative zero in signed magnitude from being trap values. This compounds the original K&R mistake of assuming that integer overflow is ignored, and is slightly in conflict with the stated intention of IEEE 754. So I suggest changing the descriptions of the sign bit to the following: - the corresponding value with sign bit zero is negated, and it is implementation-defined whether the value with sign bit one and all other bits zero is a trap value or has a value of zero; - the sign bit has value -2N, and it is implementation-defined whether the value with sign bit one and all other bits zero is a trap value or has a value of -2N; - the sign bit has value 1-2N, and it is implementation-defined whether the value with all bits one (including the sign bit) is a trap value or has a value of zero.